For many years production apparatus consisting of an extruder and a calender has been used for producing sheets and/or foils of plastic material or rubber mixtures. If a fully homogenized and disintegrated extrudant leaves the extruder head at a proper temperature, the calender serves merely as a smoothing, cooling and/or calibrating device. In this case there occurs in the roller gap, in advance of the narrowest part of the gap, merely a limited bulging of the extrudant produced by an accumulation of the extrudant in front of the narrowest part of the roller gap. As the calender, like the extruder, can carry out the work of mixing, homogenizing, disintegrating and tempering the extrudant when a considerably accumulation of material forms in front of the narrowest part of the roller gap, there occurs in the roller gap a rotary movement and kneading action, so that the accumulated material is kneaded, whereby it is possible to use in the extruder-calender combination an extruder that does not fully homogenize, mix and disintegrate the material, but a part of this work is left to the calender.
The formation and the size of the bulge of material accumulating in the roller gap is solely dependent on technical measures, namely on the relation of the amount of extruded material introduced into the roller gap to the size of the roller gap and rate of rotation of the rollers. In the production, the apparatus is adjusted in the starting process to obtain the desired size of the accumulation of material to be kneaded and during the production, the desired size of the accumulation of material is obtained through control of the forenamed parameters.
On the contrary, the thickness of the sheet or foil produced is largely dependent on the gap width of the mouth of the extruder head. Hence, for many years extruder heads have been produced with interchangeable and/or adjustable forming bars so that different thicknesses of sheets or foils could be produced. However, there is still a further reason for the removabilty of the forming bars. For the width-wise distribution of the mass, the walls of the flow paths of the extrudant in the extruder head must have a particular form which cannot always be determined purely theoretically. Hence the flow paths for the extrudant must often be altered through test runs of the production apparatus. So that the heavy extruder head parts do not have to be clamped on the reworking machine, the forming bars are removably mounted so that only the forming bars, without other parts of the extruder head, can be clamped on the reworking machine. Also with material change of the production equipment, an exchange of the forming bars can be necessary.
In order to be able to alter the contact of faces of the rollers with the kneaded material and thereby alter the disintegrating, mixing and homogenizing work carried out in the roller gap, it is known through DE-OS 24 50 225 to make a forming bar pair of the extruder head replaceable by another forming bar pair which extends further or not so far in the roller gap. These forming bar pairs can also have different gap widths for the flow of the material to be extruded. However these measures have considerable disadvantages. They make it necessary, for the exchange of the forming bar pairs, to shut down the equipment, move the calender and extruder further apart and only then carry out the exchange of extruder bars. A continual alteration during operation of the equipment is not possible.